1. Field of the Invention
This invention relates to a process for the production of alkyl oligoglucosides with a high DP degree (1.6 to 2.0), in which alkyl polyglucosides with a low DP degree (&lt;1.6) are subjected to post-polymerization, and to the use of the alkyl oligoglucosides thus produced as defoamers in machine bottle washing.
2. Discussion of Related Art
Alkyl oligoglycosides, more particularly alkyl oligoglucosides, are nonionic surfactants which are acquiring increasing significance by virtue of their excellent detergent properties and their high ecotoxicological compatibility. The production and use of these compounds have been described just recently in a number of synoptic articles, of which the articles by H. Hensen in Skin Care Forum, 1 (October 1992), D. Balzer and N. Ripke in Seifen-Ole-Fette-Wachse 118, 894 (1992) and B. Brancq in Seifen-Ole-Fette-Wachse 118, 905 (1992) are cited as representative.
Alkyl oligoglucosides are produced from fatty alcohols and glucose or glucose sirup which are acetalized in the presence of acidic catalysts. To displace the reaction equilibrium onto the product side, the less expensive component, the fatty alcohol, is normally introduced in excess and the water of reaction is continuously distilled off. Thereafter, the acidic catalyst is neutralized to avoid secondary reactions and the excess fatty alcohol is distilled off in vacuo.
Now, 1 mole of fatty alcohol and 1 mole of glucose come together non-selectively during the reaction. The glucose also undergoes likewise acid-catalyzed self-condensation in competition with the formation of these monoglucosides, resulting in the formation of polysugars. In addition, the glucose reacts with the alkyl glucosides already formed to form oligoglucosides. This results in the formation of a complex mixture of mono-, di-, tri-, tetra- and oligoglucosides which, in addition, contains considerable amounts of polyglucose. Apart from the alkyl chain length, the applicational properties of the glucosides, for example their solubility, cold cloud point, foam stability and thickenability, are also determined by the homolog distribution which is defined by a ratio known as the degree of polymerization (DP).
Commercial alkyl oligoglucosides generally have a low DP of 1.2 to 1.6. This is attributable above all to technical reasons because higher degrees of oligomerization can normally only be established when the fatty alcohol excess in the acetalization is small. However, this is only possible to a limited extent on account of the high initial viscosity of the mixtures.
Another problem is that a small excess of fatty alcohol promotes the formation of unwanted polyglucose and significantly impairs the color quality of both the bleached and the unbleached products. At the same time, however, there is a need in the market place for alkyl oligoglucosides with a high DP which can be superior in some respects to the commercial products available with their low degrees of oligomerization.
Accordingly, the complex problem addressed by the present invention was to provide a process for the production of alkyl oligoglucosides with a high degree of oligomerization by which the problems presented by the initial viscosity of the reaction mixtures, the high polysugar content and the inadequate color quality could be solved at one and the same time. In addition, in view of the occasionally inadequate alkali stability of the products, the alkyl oligoglucosides produced by the process according to the invention would have improved defoaming properties in machine bottle washing, even under strongly basic conditions.